Process for the removal of nitrogen trihalides from mixtures containing them



United States Patent Ofiice 3,361,536 Patented Jan. 2, 1968 3,361,536 PROCESS FOR THE REMOVAL OF NITROGEN TRIHALIDES FROM MIXTURES CONTAINING THEM Guy Vincotte, Tervueren, Belgium, assignor to Solvay & Cie, Brnsseis, Belgium, :1 Belgian company No Drawing. Filed Jan. 11, 1965, Ser. No. 424,851 Claims priority, application Belgium, Feb. 21, 1964, 516,955 12 Claims. (Cl. 23219) ABSTRACT OF THE DISCLOSURE Nitrogen trihalides are decomposed in mixtures containing them by contacting the mixtures with Monel metal.

The present invention concerns a process for removing nitrogen trihalides from mixtures which contain them. In particular, it concerns a process for the destruction of nitrogen trichloride contained in gas or liquid mixtures, for. example in mixtures containing liquid or gaseous chlorine and nitrogen trichloride.

It is knownthat the nitrogen triha-lides are very unstable compounds whose decomposition can often be accompanied by violent defiagration. As the nitrogen trihalides are found in a large number of mixtures which contain halogens, it is necessary to remove them because of their instability. Up until now, either thermal or photochemical processes have been used to destroy the nitrogen trihalides. These processes have not proved satisfactory because, in addition to the fact that they are expensive and difiicult to carry out, they do not lead to a complete destruction of the nitrogen trihalides, and this means that a mixture which only contains a small amount of these impurities cannot be purified.

The process which constitutes the object of the present invention makes it possible to overcome these disadvantages without having to take special measures. It leads to the complete and rapid destruction of the nitrogen trihalides even if the original mixture only contains a tiny proportion of them.

Other advantages will be description.

The applicants have found that quite unexpectedly mixtures which contain nitrogen trihalides as impurities can be simply and rapidly purified by contacting them with the nickel-copper alloy known under the name of Monel metal. This alloy is preferably applied in the form of coarse powder or, better still, in the form of turnings.

In this connection, the term Monel metal is employed to describe alloys containing 60 to 70% Ni, 25 to 35% Cu, 1 to 3% Fe, 0.25 to 2% Mn, 0.02 to 1.5% Si and 0.3 to 0.5% C (Bennett: Concise Chemical and Technical Dictionary, 1962). These alloys may possibly contain small amounts of Co and Al.

The applicants are aware of the fact that it is known how to destroy nitrogen trihalides and in particular nitrogen trichloride by means of copper or nickel; however, these metals cannot completely destroy the nitrogen trihalides and their action is rather slow. It was not possible to foresee that the combination of copper and nickel in Monel metal would provide the results observed evident from the following by the applicants, because the results indicate a considerable synergistic effect, particularly in respect of a synthetic copper-nickel mixture. These eifects will be demonstrated below.

The process which constitutes the object of the invention is carried out in an exceedingly simple manner: In the case of gaseous mixtures, it is suflicient to let them pass over a filter consisting of piles of turnings or coarse grains of Monel metal. In the case of a liquid, a certain amount of Monel metal turnings are introduced into the medium and it is allowed to react for a given period.

The alloy remains active for a long time and can readily be regenerated by treating it with water in order to dissolve off the salts formed on its surface before it is dried by a suitable method (for instance by treating it with acetone and airing in a current of air).

The applicants have also found that if the liquid or gaseous chlorine contains an amount of bromine greater than p.p.m. it is convenient to submit it to a preliminary debromination treatment in order to reduce the bromine content to a value less than 100 p.p.m. in order to derive the full benefit of the process which constitutes the object of the present invention.

vT he invention is to be explained by reference to the following Examples given by way of illustration, and although these examples deal with the purification of chlorine by the removal of nitrogen trichloride, they do not in any way limit the scope of the invention.

EXAMPLE 1 This example is given by way of comparison; it concerns the treatment of gaseous chlorine containing variable amounts of nitrogen trichloride (expressed in parts per million) by means of copper turnings, nickel turnings and a mixture of copper and nickel turnings, the copper and nickel being in the proportion of 30:70 by weight, i.e. very substantially in the proportion of these metals in Monel metal.

The filter employed has a height of mm. and a diameter of 45 mm. The rate of flow of the chlorine is 20 CIlL/SEC. The operation is carried out at room temperature.

When the amount of nitrogen trichloride falls below a certain level, the efiect of copper, of nickel and of a copper-nickel mixture tends to zero.

- 3 EXAMPLE 2 The same conditions as in Example 1 are observed but the filtering element used to fill the filter consists of turnings of Monel metal of the composition Ni 65%, Cu 31%, Fe 1.5%, Si 0.3%, Mn 0.8%, C 0.2% and Co 0.4%.

N01 p.p.m.

After filtration Before filtration After filtration B elore filtration At the selected rate of flow, i.e. at 20 cm./ sec. which corresponds to a period of contact of about 0.6 second, the destruction of nitrogen trichloride is complete provided that its content does not exceed about 250 ppm. When its content is greater, it is sufiicient to extend the period of contact between the gas mixture and the filter by a suitable method.

The process has been successfully employed in an industrial plant. A filter of diameter 150 mm. and height 500 mm. has been fitted on the collector of concentrated chlorine from an electrolytic cell with a mercury cathode. The nitrogen trichloride content of the concentrated chlorine had varied between 3 and 6 p.p.m.

At the end of 10 weeks, 231 tons of chlorine had been treated and the destruction of the nitrogen trichloride remained complete. It is not possible to obtain a similar result by means of the previously known processes.

EXAMPLE 3 This example deals with the destruction of nitrogen trichloride in liquid chlorine. For this purpose, Monel metal turnings are introduced into liquid chlorine and the reaction is allowed to continue until the instant when the destruction of the nitrogen trichlorideis complete.

7 N01 ppm.

Itis evident that it is preferable to treat the chlorine whilst in the gaseous state in order to prevent the occurrence of nitrogen trichloride in liquid chlorine because the complete destruction of the impurity is then more rapid. Nevertheless, the above example shows that the process can be applied in the case of liquid chlorine and that if for any reason it should be necessary to evacuate completely a reservoir containing liquid chlorine (for instance in order to carry out repairs: welding, etc.) the presence of nitrogen trichloride, which in the past has required the institution of special precautions (for instance washing with chlorinated solvents), no longer presents any problems.

I claim:

1. Process for the decomposition of nitrogen trichloride in a mixture containing it as an impurity, comprising contacting said mixture with a natural alloy known as Monel metal, said alloy being in the form of particles and containing 60 to Ni, 25 to 35% Cu, 1 to 3% Fe, 0.25 to 2% Mn, 0.02 to 1.5% Si and 0.2 to 0.5% C, whereby nitrogen trichloride is decomposed and removed from said mixture and recovering the thus-purified mixture.

2. Process according to claim 1, in which the particles are turnings.

3. Process according to claim 1, in which the particles are coarse powder.

4. Process according to claim 1, in which the mixture containing the nitrogen trichloride is gaseous and said contacting comprises passing said gaseous mixture over a filter comprised of particles of said alloy.

5. Process according to claim 1, in which the mixture containing the nitrogen trichloride is liquid and said contacting comprises adding particles of said alloy to said liquid mixture.

6. Process according to claim 5, in which the particles are turnings. V p g V 7. Process according to claim 1, in which said mixture is comprised of liquid chlorine and said nitrogen trichloride and said contacting comprises placing particles of said alloy in said mixture. 7

8. Process according to claim 7, in which said mixture is further comprised of bromine and said mixture is subjected to a preliminary debromination treatment in order to reduce its bromine content to a value less than ppm.

9. Process for purifying chlorine according to claim 1, in which said mixture is comprised of gaseous chlorine and said nitrogen trichloride impurity, in which said contacting comprises passing said mixture over particles of said alloy, and in which purified chlorine is recovered.

10. Process according to claim 9, in which the period of contact is set at a sufiicient magnitude for the essentially complete destruction of the nitrogen trichloride, said period being proportional to the content of the nitrogen.

trichloride in said mixture. 2

11. Process according to claim 10, in which the period of contact is about 0.6 second provided that the content of nitrogen trichloride in the chlorine is not greater than 12. Process according to claim 9, in which said mixture is further comprised of bromine and said mixture is subjected to a preliminary debromination treatment in order to reduce its bromine content to a value less than 100 ppm.

References Cited UNITED STATES PATENTS 1,934,795 11/1933 Frazer 232 X 2,692,818 10/1954 Bewick 23219 2,731,329 1/1956 Kamlet ..Q 23'2l9 OTHER REFERENCES I. W. Mellors A Comprehensive Treatise on Inorganic and Theoretical Chem., vol. 8, 1928 ed., pp. 603

and 604. Longmans, Green and Co., New York, pub- MILTON WEISSMAN, Primary Examiner.

EDWARD STERN, Examineiz 

